Removable bearing assembly for tunneling machine

ABSTRACT

An easily replaceable bearing assembly for a tunneling machine including a housing, a rotor within the housing, radial bearings for supporting respective ends of the rotor from the housing, a thrust bearing intermediate the radial bearings and disposed between respective thrust collars on the housing and rotor so that a forward thrust on the housing can drive the rotor forward, removable means for applying a forward drive to the rearward end of the housing and a rotating drive to the rearward end of the rotor, and means for attaching a rotating cutter to the forward end of the rotor so as to be concurrently driven forwardly and in rotation.

llited States Patent 11 1 Safar 51 June 5, 1973 541 REMOVABLE BEARINGASSEMBLY 2,756,036 7/1956 Mclntyre ..299 31 x FOR TUNNELING MACHINE1,232,750 7/1917 Amess ..308/175 X [75] Inventor: Frank Saiar,Fullerton, Calif. Primary Examiner Emest R. Purser [73] Assignee: SmithInternational, Inc., Newport Att0rney-Beehler,Arant&Jagger Beach, Calif22 Filed: Aug. 30, 1971 [57] ABSTRACT An easily replaceable bearingassembly for a tunneling [21] Appl' 175824 machine including a housing,a rotor within the hous Related US, A li ti D t ing, radial bearings forsupporting respective ends of 62 the rotor from the housing, a thrustbearing inter- 1 Dw'slon ofser 8637810 1969' mediate the radial bearingsand disposed between respective thrust collars on the housing and rotorso 2? 43 33 32 3;g figzi that a forward thrust on the housing can drivethe l58l F It! 299/3; 33 59 rotor forward, removable means for applyinga for- 0 174 /5 ward drive to the rearward end of the housing and arotating drive to the rearward end of the rotor, and means for attachinga rotating cutter to the forward [56] References Cned end of the rotorso as to be concurrently driven for- UNITED STATES PATENTS wardly and inrotation- 2,991,058 7/1961 Alspaugh et al ....299/57 6 Claims, 4 DrawingFigures PATENTEDJUH 5 I975 SHEET 1 [IF 4 PATENTEDJUN 5|975 3.736.771

SHEET 2 OF 4 INVENTOR.

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SHEET U 0F 4 INVENTOR. F64/VA $454.2

% aw/M REMOVABLE BEARING ASSEMBLY FOR TUNNELING MACHINE This applicationis a division of my prior copending application, Ser. No. 863,783, filedOct. 6, 1969.

BACKGROUND OF THE INVENTION The present invention relates to replaceablebearing assemblies for tunneling machines having a rotary boring head orcutter for cutting passages through hard rock and minerals. Machines ofthis type frequently bear stress loads of a million pounds or more. Thehigh degree of hardness of material being cut reflects a heavy stressload on the boring head or cutter, and this stress load in turn must becarried by a bearing mechanism which permits the boring head or cutterto rotate, and must also be transmitted to other supporting portions ofthe machine.

It is well known in the art in a machine of this type to utilize a mainsupport frame and a movable frame, which are longitudinally movablerelative to each other, thus permitting a stepwise advance of themachine in a forwardly direction as the tunnel is being cut. The mainframe typically has a set of forward shoes and a set of rearward shoes,each of which may be extended for supportive engagement with the tunnelwall. The movable frame also has a forward shoe and a rearward shoewhich support both frames during the time when the main support frame isbeing relocated in the tunnel.

Heretofore, the machines of this general type have suffered from a veryshort useful life before rebuilding or major repair has been required.The primary object and purpose of the present invention is to provide areplaceable bearing assembly for a machine of the type described, whichhas a long useful life before rebuilding or repairs are required.

The present invention provides a replaceable bearing assembly for atunneling machine comprising: a hollow housing having a generallycylindrical configuration and having means on its rearward end adaptedfor removable attachment of said housing to the forward end of a movablesupport frame, said housing having on its interior surface a thrustcollar located intermediate to its forward and rearward ends, saidinterior thrust collar having a forwardly facing thrust shoulder, arotor disposed within said housing, said rotor having on its forward endmeans for removably attaching a rotating cutter thereto, having on itsrearward end means for coupling a drive shaft thereto, and having on itsexterior surface a thrust collar with a rearwardly facing thrustshoulder, a thrust bearing disposed between said interior thrust collarof said housing and said thrust collar of said rotor, whereby forwardthrust exerted against said housing may be imparted to said rotor, and apair of radial bearings disposed between said housing and said rotor,one at the forward end and the other at the rearward end, wherebyrotating thrust from said drive shaft may be concurrently imparted tosaid cutting wheel.

In the drawings:

FIG. 1 is a schematic diagram showing the main operative parts of themachine;

FIG. 2 is a side elevational view of a tunneling machine in accordancewith the present invention, located in a cutting position within atunnel;

FIG. 3 is a vertical cross-sectional view of the machine taken on theline 3-3 of FIG. 2;

FIG. 4 is a longitudinal cross-sectional view of the front end portionof the machine.

The tunneling machine of the present invention will first be generallydescribed with reference to FIG. 1 of the drawings.

The tunneling machine includes a main support frame 50 having fronttelescoping legs 60 and rear telescoping legs 65 which are adapted foroutward extension to grip the tunnel wall. Thrust cylinders carried atthe forward end of main support frame 50 provide a forward thrust drivemeans and are expanded for driving the operative portions of the machinein a forwardly direction so as to force the cutter 300 against the endface of the tunnel.

A movable frame is disposed within the main support frame 50, and islongitudinally movable relative to the main support frame. All of theoperative portions of the tunneling machine are connected or coupled,either directly or indirectly, to the movable frame 110. Thus themachine as a whole can be advanced stepwise in the forwardly direction.The procedure is that the main support frame 50 is located in aparticular longitudinal position within the tunnel; the telescoping legs60 and 65 are extended into engagement with the tunnel walls so as torigidly support the main support frame in that location; and the thrustcylinders 80 are then expanded forwardly until a particular cuttingstroke has been completed. Auxiliary shoes 160 and 165, associated withthe forward and rearward ends, respectively of the movable frame 110 arethen used for supporting the entire machine while the main support frame50 is being relocated to a more forwardly advanced position. Thisgeneral mode of advancing the machine is well known in the art and henceneed not be described in further detail.

Although the specific mechanism is not shown in FIG. 1, the movableframe 110 is supported in a nonrotative relationship to the main supportframe 50, but is free to move longitudinally relative to the mainsupport frame 50, and is preferably supported in a longitudinal slidingrelationship relative to the main frame 50.

A main drive shaft 130 is disposed inside the movable frame 110, and isadvanced along the tunnel in conjunction with movement of the movableframe. A rear bearing supports the rearward end of drive shaft forrotation relative to movable frame 110. A gear box is attached to therearward end of movable frame 110, and is also coupled to the rearwardend of the main drive shaft 130. A drive motor associated with gear box135 is operable for imparting a rotating drive to the drive shaft 130,so that the drive shaft will rotate relative to the movable frame 110.The rear auxiliary shoe 165, although it could be attached directly tothe rearward end of movable frame 110, is for convenience attachedunderneath gear box 135.

To complete the rotating drive mechanism a pair of driving gears 150,155 are located at the forward end of the main drive shaft 130. Thedrive gear is a male gear which is rigidly attached to the forward endof drive shaft 130. The driving gear is a female gear which is rigidly(but removably) attached to the rotor 220 of main bearing assembly 200.An important feature of the present invention is that the female gear155 is free to slide longitudinally, at least to some extent, relativeto the male drive gear 150. The significance of that feature of themachine will be described subsequently.

A main bearing assembly 200 is used to support and to drive the cutter300, and concurrently receives both the forward thrust drive from thrustcylinders 80 and the rotating drive from drive shaft 130. The mainbearing assembly 200 includes a housing or stator 210 which is of agenerally hollow cylindrical configuration. A rotor 220 is disposedconcentrically within the housing 210, and is supported for rotationrelative to the housing by means of a front end radial bearing 240 and arear end radial bearing 250. Removable attachment means such as bolts221 are employed for removably attaching the female drive gear 155 tothe rearward end of rotor 220. Removable attachment means such as bolts222 are used for removably attaching the cutter 300 to the forward endof rotor 220.

The rearward end of housing or stator 210 is removably attached to theforward end of movable frame 110, as by means of bolts 211. The forwardthrust of the thrust cylinders 80 is applied to a thrust collar 215formed on the housing 210, hence the forward thrust of the thrustcylinders 80 serves to pull the movable frame 110 in a forwardlydirection.

Also located between the housing 210 and the rotor 220 is a thrustbearing 230, which is disposed intermediate to the forward and rearwardend bearings. The

. function of the thrust bearing 230 is to impart a forward thrust drivefrom the housing or stator 210 into the rotor 220. The associatedmechanism includes an interior thrust collar 217 on the housing 210which has a forwardly facing thrust shoulder, and an exterior thrustcollar 225 on the rotor 220 which has a rearwardly facing thrustshoulder, the thrust bearing 230 being supported between these twothrust shoulders.

The forward auxiliary shoe 160, although it could be attached directlyto the forward end of movable frame 110, is for convenience attachedunder the housing 210.

During a cutting operation of the machine the cutter 300 receives bothrotational and thrust loadings which vary over a wide range in a ratherunpredictable manner, with the peak loadings being very high. In most orall of the prior art machines for tunneling in hard rock or hardminerals, the longitudinal thrust force of the machine as well asvibrational stresses are imparted through the main drive shaft into therotating drive mechanism. According to the present invention, however,the female drive gear 155 is longitudinally slidable relative to themale drive gear 150, hence the longitudinal and vibrational stressesimparted from cutter 300 to rotor 220 are not transmitted to the driveshaft 130, except perhaps with a greatly reduced magnitude. The gear box1135 is thus protected from any extraneous interference, and is free toperform its simple function of imparting a rotating drive to the driveshaft 130, under conditions which permit it to have a long useful lifeand to operate relatively free of maintenance requirements.

Another significant feature of the invention is that the main bearingassembly 200 is arranged for easy removal, in its entirety, from thetunneling machine. Thus the coupling of thrust cylinders 80 to thethrust collar 215 of housing 210 is such as to permit easy detachment ofthe housing 210 from the thrust cylinders. Removable bolts 211 alsopermit easy detachment of housing 210 from the movable frame 110.Removable bolts 221 permit easy detachment of female drive gear 155 fromrotor 220, and removable bolts 222 permit easy detachment of cuttingwheel 30% from the rotor. The radial bearings 240 and 250, and thethrust bearing 230, involve a large number of individual parts, andthese bearing mechanisms tend to wear during operation of the machine.The easily removable nature of the attachments of housing or stator 210and of rotor 220 to the other parts of the machine makes it possible toremove the entire main bearing assembly 200 as a unit. A new mainbearing assembly may be inserted in the tunneling machine withcomparatively small loss of working time. The worn or damaged mainbearing assembly may then be transported away from the construction jobto a shop or factory where its repair or overhaul may be conducted on amore leisurely basis.

In utilizing the tunneling machine of the present invention it may bepreferred, however, to replace the main bearing assembly 200periodically as a preventive maintenance feature. In that case, the mainbearing assembly which is removed may not be significantly worn ordamaged at all, but replacing the old assembly with a new one involvesonly a short down time for the machine and insures a long uninterruptedoperating time for the machine when its usage is resumed.

The presently preferred embodiment of the invention, as illustrated indrawing FIGS. 2, 3 and 4, inclusive, will now be described in somedetail.

The structure and operation of the machine has already been describedwith reference to FIG. 1, where the various component parts of themachine are illustrated schematically, rather than in accordance withtheir precise mechanical construction. The reference numbers used inFIG. 1 are also applied to the corresponding parts of the machine inFIGS. 2, 3 and 4, hence it will be understood that in FIG. I theparticular reference number applies to a schematic representation of thepart, whereas in FIGS. 2, 3 and 4, the same reference number indicatesthe actually preferred, precise form of the same part.

The schematic representation of the machine in FIG. I ignores the factthat in addition to the cutter which may take the form of a circularmain cutting wheel 300 the machine also includes a center drill 400. Thedetailed drawings illustrate a drive mechanism and a bearing supportassembly for the center drill, which are concentrically arrangedrelative to the main drive shaft and main bearing assembly. Before goinginto a detailed description of the center drill and its associatedbearing assembly and drive mechanism, however, it will be advantageousto describe in detail the main portions of the machine which havealready been discussed in connection with FIG. ll.

Thus the main support frame 50 has a square crosssectional configurationand is formed of two separate frame halves 52, 5d which are joinedtogether by bolts 58 (FIG. 35). Each of the telescoping front legs 60has a leg base 62 onto which ribs 56 are attached for purposes ofstructural reinforcement. Similar rib structures are also associatedwith the leg bases 67 of the rear telescoping legs 65. Wear bars 70 areattached to the interior corners of the housing structure 52-54 andprovide surfaces within which the guide tube 115 may slidelongitudinally. The wear bars 70 are preferably made of machined brassmaterial.

The actual physical structure of movable frame includes a guide tubewhose cross-sectional configuratiois in the form of a hollow square(FIG. 3) and which extends throughout the greater part of the length ofthe machine. The exterior corner surfaces of guide tube 115 slide withinthe wear bars 70, the wear bars being located at both the forward andthe rearward ends of housing 50. A circular ring 117 is welded onto theforward end of guide tube 115 (FIG. 4) and forms the forward end portionof movable frame 110. A circular ring 119 is welded to the rearward endof guide tube 115 and forms the rearward end portion of mov ableconfiguration 110.

A front bellows 75 and a rear bellows 77 constitute, in a sense,extensions of the main support frame 50 (FIG. 2). The purpose of thesebellows is to prevent dirt and other foreign materials from enteringinto the interior spaces between housing 50 and guide tube 1 15, inwhich a precisely controlled longitudinal sliding action of the movableframe 110 needs to be achieved. The front bellows 75 therefore has itsrearward end attached to the front end of housing 50 and its forward endattached to the guide tube forward ring 117 (FIG. 4). The rear bellows77 has its forward end attached to the rearward end of housing 50 whileits rearward end is attached to the gear box 135 (FIG. 2).

There are four of the thrust cylinders 80 located at the top, bottom,and sides of main support frame 50 (FIG. 3). Each thrust cylinder has anassociated cylinder rod 83 which is extendable in the forward'directionfor imparting the thrust force. A removable thrust collar 85 slides overthe rearward portion of housing 210 of the main bearing assembly (FIG.2) and has circumferentially spaced ears 86 in which pins 87 arecarried, each pin 87 being pivotally connected to the forward end of theassociated rod 83. Removable bolts are used to attach to forward end ofthrust collar 85 to the thrust collar 215 of housing 210.

The main drive motor 140 which is schematically illustrated in FIG. 1 bya single-block is in fact a group of six separate motors disposed aboutthe periphery of gear-box 135 (FIG. 2). Each of these motors drives abull gear 137 (not shown) which is attached to the rearward end of driveshaft 130. During cutting operations of the machine the forward end ofdrive shaft 130 is supported by the gears 150, 155. When the mainbearing assembly 200 is removed from the machine, however, it becomesnecessary to indiepndently support the front end of the drive shaft, andfor this purpose a support ring 127 is provided within the forward endof guide tube 115.

In the main bearing assembly the front radial bearing 240 has an innerring or raceway 242, an outer ring or raceway 246, and cylindricalbearings 244 which are retained between the two raceways. A frontbearing retainer 260 is attached both to the housing 210 and to therotor 220 for shielding the bearing 240 from dirt.

Rear radial bearing 250 includes an inner ring or raceway 252, an outerring or raceway 256, and cylindrical bearings 254 which are disposedbetween and retained by the two raceways. There are two separateretainers for the rear bearing, the outer one being designated as 270and the inner one as 280 (FIG. 4). A rotary seal 275 is located betweenretainers 270, 280.

Thrust bearing 230 includes a rear thrust plate or ring 231 which issupported from the thrust collar 217 of housing 210. A bearing cage 233(FIG. 4) has radial legs, and on each radial leg there are threecylindrical bearing members 234 disposed for rotation. The thrust ringor plate 231 lies in a plane that is transverse to the longitudinal axisof rotor 220, and the outer circumferential surface of ring 231 firmlyengages the interior wall surface of housing 210 while its innercircumferential surface is spaced away from the rotor 220. Thecylindrical bearing members 234 ride on the forward flat surface of therear pressure plate 231, and also ride on the rear flat surface of therear pressure plate 231, and also ride on the rear flat surface of aforward pressure plate 235. Pressure plate 235 is disposed parallel tothe pressure plate 231, having its interior circumferential surface infirm engagement with the exterior surface of rotor 220 to rotatetherewith while its outer circumferential surface is spaced away fromhousing 210. The forward flat surface of pressure ring 235 bears againsta spacer ring 225.

It will be noted that in FIG. 1 the reference numeral 225 applies to apart which is schematically illustrated as a thrust collar formed on theexterior surface of rotor 220. In the preferred embodiment of theinvention, however, the member 225 is in fact a spacer ring which isslid over the exterior surface of rotor 220, the forward edge of thespacer ring being lodged against inner raceway 242 of the front radialbearing 240. The raceway 242 is, in turn, lodged against a shoulder 226of rotor 220. Hence, the spacer ring 225 is supported against forwardmotion relative to the rotor 220, and forward thrust bearing 230 isoperative to impart forward thrust from housing 210 into the rotor 220in the manner which is schematically illustrated in FIG. 1.

The tunneling machine of the present invention is designed for a forwardloading on the cutting wheel of approximately one million pounds, andthis forward loading is also carried by the thrust bearing 230, thusinvolving the possibility of a substantial deformation of the componentparts of the thrust bearing and associated mechanism. Before placing themachine in operation the parts are aligned in such a way that the rearthrust plate 231 of thrust bearing 230 is spaced a predetermined amount,such as 0.030 inches, from the thrust collar 217 of housing 210. Aplurality of recesses 218 are formed in the thrust collar 217, and aseparate com pression spring 232 is places within each of the recesses218 so as to provide a forward pressure against the thrust plate 231.Associated peep holes 212 are formed in the housing 210 so that theinitial spacing between thrust plate 231 and thrust collar 217 can beobserved, measured, and hence established at its proper value.

The main cutting sheel 300 includes a central hub portion 310 which ismachined so as to fit precisely over the forward end of rotor 220. Theouter or main part of the cutting wheel and the hub portion are weldedtogether to form an integral structure. A number of bolts pass throughcorresponding openings in hub portion 310 and into appropriately locatedthreaded openings of the rotor 220. Cutters 320 are mounted about thecircumference and face of the cutting wheel 300, as shown in FIG. 2. Inthe preferred embodiment of the invention there may typically be 31 ofthese cutters.

The thrust cylinders which are used to drive the machine forward duringits cutting stroke may also be used for retracting the cutting wheel 300away from the tunnel face. Bolts connecting thrust collar 215 to thrustcollar provide a positive coupling to the main bearing housing 210 sothat it may be withdrawn in the rearward direction. Thrust bearing 230is effective for thrusting the rotor 220 forward but is not effective inretracting the rotor. However, rear bearing 250 in conjunction with theinner bearing retainer 200 is effective to impart a withdrawing motionfrom the housing 210 to the rotor 220. The rearward motion of housing210 is imparted through radial bearing 250 to the outer circumferentialportion of bearing retainer 280. The inner circumferential portion ofbearing retainer 280 is fastened to rotor 220 by means of bolts 281(FIG. 1) and is therefore effective to withdraw the rotor 220. Thus awithdrawing action of the thrust cylinders 80 is effective to withdrawcutting wheel 300 from the tunnel face.

The main drive shaft 130 is hollow (FIGS. 3 and 4) thus permitting acenter drill drive shaft 410 to pass through its entire length. Aseparate drive motor 420 mounted on gear box 135 (FIG. 2) drives thecenter drill drive shaft 410 relative to the movable frame 1 10. Acenter drill bearing assembly 450 (FIG. 4), which is generally similarto the main bearing assembly 200, supports the center drill 400 to bedriven by the center drill drive shaft 410.

More specifically, the center drill bearing assembly 450 includes arotor 460 having on its rearward end the male portion 461 of a splinedcoupling. The female portion 411 is attached to the forward end of thedrive shaft 410. The splined coupling permits a longitudinal slidingrelationship between drive shaft 410 and rotor 460. The forward end ofrotor 460 projects beyond the hub 310 of the main cutting wheel andprovides a hub or base for attachment of the center drill 400.

Center drill bearing assembly 450 also includes a housing 470 that isreceived within a forward recess 227 formed in the rotor 220, androtates with the rotor 220. Lugs 471 (FIG. 4) attached to the forwardend of housing 470 are received in small circumferentially spacedrecesses in the hub 310. Bolts 472 which pass through the lugs 471permit housing 470 to slide longitudinally relative to rotor 220. Thusthe housing 470 of the center drill bearing assembly rotates with rotor220 of the main bearing assembly, while the rotor 460 is directly drivenby shaft 410.

Rotor 460 is supported for rotation relative to housing 470 by a frontradial bearing 480 and a rear radial bearing 490, and while thestructure of these radial bearings is not identical to the structure ofradial bearings 240 and 250 their operation is nevertheless very muchthe same. A front bearing retianer 482 is attached around hub 462 andextends to the forward end of housing 470 so as to protect radialbearing 480 from dirt. A thrust bearing 485 is located intermediate tothe radial bearings 480 and 490, and its structure and function are verymuch like that of the thrust bearing 230 which was previously described.That is, forward thrust received from the housing 470 is impartedthrough thrust bearing 485 into rotor 460 and hence into the centerdrill 400.

In accordance with the preferred usage of the machine the main cuttingwheel 300 is driven at a relatively slow rate, such as revolutions perminute, while the center drill 400 is driven at a more rapid rate, suchas 30 revolutions per minute. By reversing motor 420 the center drill400 may, if desired, be rotated opposite to the main cutting wheel.

The center drill bearing assembly 450 also includes a preloadingmechanism which has no counterpart in the main bearing assembly 200. Therotor 220 has a cylindrical recess 227 formed in its forward end (FIG.4), and the depth of the recess 227 is considerably greater than what isnecessary to accommodate the housing 470 of the center drill bearingassembly. The preloading assembly generally designated as 500 includes aforward plate 501 which is of generally circular configuration, buthaving a central opening through which the female coupling 411 extends.The preloading assembly 500 also includes a generally circular rearplate 502. A plurality of bolts 503 are spaced about the circumferencesof the two plates 501, 502 and are utilized to retain these plates inproximity to each other. The plate 502 has a central opening whichsurrounds the drive shaft 410, but not in direct engagement with it, sothat drive shaft 410 is permitted to rotate relative to the plate 502.To the rear of recess 227 the rotor 220 is further recessed, with asmaller diameter opening, in order to permit the pilot drill drive shaft410 to be received therein. Thus the recess 227 forms a circumferentialshoulder which faces in a forwardly direction within the rotor 220. Theouter circumferential edge of plate 502 bears against thiscircumferential shoulder and thus provides the basis for supportingcenter drill 400 for forward thrust. The inner circumferential portionof plate 502 is recessed on its front side so as to receive a'set ofBelleville disc springs 504. The springs 504 push the plate 501 forwardrelative to the plate 502, but the total displacement is limited by thebolts 503. The forward surface of plate 501 bears tight against therearward end of housing 470 (except for a bearing retainertherebetween). Y

The entire housing 470 of the center drill bearing assembly 450 is freeto slide longitudinally, to some extent, relative to the rotor 220 andhub 310. Lugs 471 are welded to the housing 470 and hence move with thehousing. Bolts 472 are firmly retained in threaded openings in the rotor220 and in the hub 310, but the openings through which they pass in thelugs 471 are not threaded, hence the lugs 471 may slide rearwardly alimited distance relative to the bolts 472.

The purpose of the preloading assembly 500 is to permit the center drill400 to retract under excessive load. For example, when the machine isbuilt with a cutting wheel diameter of thirteen feet and is designed fora total thrust of one million pounds against the tunnel face, forcutting material which has a compressive strength of 30,000 pounds persquare inch, the design load for the center drill 400 is then 90,000pounds of forward thrust. The preload assembly 500 is then set to thisload value of 90,000 pounds, and in the event the center drill receivesa load in excess of that amount it will move rearwardly a small distancerelative to the main cutting wheel 300, thus minimizing the shock on thecenter drill and protecting it against damage.

The preloading is accomplished by placing the springs 504 under acompressive stress of 90,000 pounds and then tightening the bolts 503 sothat the plates 501, 502 will retain the springs in their compressedcondition. A gap 505 between plates 501, 502 would permit furthercompression of the springs 504. However, under normal operatingconditions the thrust load on the center drill is 90,000 pounds or less,hence the springs 504 are not required to accept any additionalcompression and the gap 505 does not close even partially. But if anoverload for the center drill is encountered then that overload will bepicked up by the springs 504, and the center drill together with itsbearing assembly 450 will be permitted to retract relative to the maincutting wheel. Lugs 471 will move rearwardly relative to hub 310 and thegap 505 will commence to close.

For purpose of moving the machine into and out of a tunnel, andtransporting it, it is necessary to disassemble the main cutting wheel300. With reference to FIG. 4, there is illustrated a removable spoke330 of the main cutting wheel, which can be detached from the centralportion of the cutting wheel simply by removing a number of bolts. Thisillustrated detail is typical of the cutting wheel construction andindicates the manner in which the entire cutting wheel may bedisassembled for convenience in transportation.

It is possible to remove and replace both the main bearing assembly 200and the center drill bearing as sembly 450 in a very limited time, suchas two or or three hours where an overload crane and other shopequipment are available, or perhaps two or three days under conditionswhich prevail inside a tunnel. The procedure for removing and replacingthese two bearings will now be briefly described.

First the entire machine is retracted from the tunnel face, a distanceof about ten feet. Then the center drill 400 and its bearing assembly450 are removed. This is accomplished simply by removing the nuts fromthe bolts 472, and the entire housing 470 together with the associatedpreload assembly 500 slides out of recess 227 of the rotor 220. Thesplined coupling 461, 411 simply separates.

The next step is to remove the main cutting wheel 300. This is done byremoving the bolts connecting the wheel and rotor 220. The hub 310 thensimply slips off the forward of rotor 220. The next step is to expandthe thrust cylinders 80 so as to move the movable frame 1 10 about 2feet forward from its most rearwardly position. Access can then beobtained to the bolts 211, of which in the presently preferred form ofthe machine there are 48 spaced about the periphery of the front guidetube ring 117.

Thereafter, the bolts 88 are removed and the thrust cylinders 80 areretracted so as to draw the thrust collar 85 rearwardly. It is thenpossible to pull the main bearing assembly 200 in a forwardly directionand remove it from contact both with the guide tube flange 117 and withthe thrust collar 85. The female gear 155 may then be detached fromrotor 220 by removing the bolts 221.

As a convenience in performing these operations it is desirable toprovide a small rearward extension (not shown in the present drawings)on thrust collar 85. This extension serves to support the thrust collar85 from the guide tube ring 117 both during and after the time when thebolts 211 are removed. Another desirable convenience is a platform whichcan be positioned in front of the machine to receive the main bearingassembly 200 when it is removed.

The female drive gear may be attached to the replacement main bearingunit, which can then be inserted into the machine by following thereverse of the procedure described above. After the main bearingassembly has been replaced a new pilot drill bearing assembly isinserted, again by following the reverse of the described procedure.

I claim:

1. A replaceable bearing assembly for a tunneling machine comprising: ahollow housing having a generally cylindrical configuration and havingmeans on its rearward end adapted for removable attachment of saidhousing to the forward end of a movable support frame; said housinghaving on its interior surface a thrust collar located intermediate toits forward and rearward ends, said interior thrust collar having aforwardly facing thrust shoulder; a rotor disposed within said housing,said rotor having on its forward end means for removably attaching arotating cutter thereto, having on its rearward end means for coupling adrive shaft thereto, and having on its exterior surface a thrust collarwith a rearwardly facing thrust shoulder; a thrust bearing disposedbetween said interior thrust collar of said housing'and said thrustcollar of said rotor, whereby forward thrust exerted against saidhousing may be imparted to said rotor; and a pair of radial bearingsdisposed between said housing and said rotor, one at the forward end andthe other at the rearward end, whereby rotating thrust from said driveshaft may be concurrently imparted to said cutting wheel; the forwardand rearward ends of said housing and said rotor being essentiallycoterminous whereby said assembly may be conveniently removed andreplaced as a unit.

2. The bearing assembly of claim 1 wherein said rotor has a cylindricalrecess centrally located in its forward end, and a smaller diameteropening extending from said recess to the rearward end of said rotor.

3'. A bearing assembly as claimed in claim 1 wherein said movablesupport frame is a pre-loaded assembly including a forward plate, arearward plate, spring means compressed between said plates, andretaining means limiting the separation of said plates.

4. The bearing assembly of claim 1 wherein said drive shaft couplingmeans includes intermeshed gears which are slidable relative to eachother along the longitudinal axis of said rotor.

5. The bearing assembly of claim 1, wherein said housing also has on itsexterior surface a thrust collar having a rearwardly facing thrustshoulder.

6. The bearing assembly of claim 2 wherein said interior thrust shoulderof said housing is located forwardly of said exterior thrust shoulderthereof.

l t I t t

1. A replaceable bearing assembly for a tunneling machine comprising: ahollow housing having a generally cylindrical configuration and havingmeans on its rearward end adapted for removable attachment of saidhousing to the forward end of a movable support frame; said housinghaving on its interior surface a thrust collar located intermediate toits forward and rearward ends, said interior thrust collar having aforwardly facing thrust shoulder; a rotor disposed within said housing,said rotor having on its forward end means for removably attaching arotating cutter thereto, having on its rearward end means for coupling adrive shaft thereto, and having on its exterior surface a thrust collarwith a rearwardly facing thrust shoulder; a thrust bearing disposedbetween said interior thrust collar of said housing and said thrustcollar of said rotor, whereby forward thrust exerted against saidhousing may be imparted to said rotor; and a pair of radial bearingsdisposed between said housing and said rotor, one at the forward end andthe other at the rearward end, whereby rotating thrust from said driveshaft may be concurrently imparted to said cutting wheel; the forwardand rearward ends of said housing and said rotor being essentiallycoterminous whereby said assembly may be conveniently removed andreplaced as a unit.
 2. The bearing assembly of claim 1 wherein saidrotor has a cylindrical recess centrally located in its forward end, anda smaller diameter opening extending from said recess to the rearwardend of said rotor.
 3. A bearing assembly as claimed in claim 1 whereinsaid movable support frame is a pre-loaded assembly including a forwardplate, a rearward plate, spring means compressed between said plates,and retaining means limiting the separation of said plates.
 4. Thebearing assembly of claim 1 wherein said drive shaft coupling meansincludes intermeshed gears which are slidable relative to each otheralong the longitudinal axis of said rotor.
 5. The bearing assembly ofclaim 1, wherein said housing also has on its exterior surface a thrustcollar having a rearwardly facing thrust shoulder.
 6. The bearingassembly of claim 2 wherein said interior thrust shoulder of saidhousing is located forwardly of said exterior thrust shoulder thereof.